class ChapterRecognition {
  final _numberPattern = r"([0-9]+)(\.[0-9]+)?(\.?[a-z]+)?";

  final _unwanted = RegExp(r"\b(?:v|ver|vol|version|volume|season|s)[^a-z]?[0-9]+");

  final _unwantedWhiteSpace = RegExp(r"\s(?=extra|special|omake)");

  int parseChapterNumber(String mangaTitle, String chapterName) {
    var name = chapterName.toLowerCase();

    name = name.replaceAll(mangaTitle.toLowerCase(), "").trim();

    name = name.replaceAll(',', '.').replaceAll('-', '.');

    name = name.replaceAll(_unwantedWhiteSpace, "");

    name = name.replaceAll(_unwanted, "");
    final numberPat = "*$_numberPattern";
    const ch = r"(?<=ch\.)";
    var match = RegExp("$ch $numberPat").firstMatch(name);
    if (match != null) {
      return _getChapterNumberFromMatch(match).toInt();
    }

    match = RegExp(_numberPattern).firstMatch(name);
    if (match != null) {
      return _getChapterNumberFromMatch(match).toInt();
    }

    return 0;
  }

  double _getChapterNumberFromMatch(Match match) {
    final initial = double.parse(match.group(1)!);
    final subChapterDecimal = match.group(2);
    final subChapterAlpha = match.group(3);
    final addition = _checkForDecimal(subChapterDecimal, subChapterAlpha);
    return initial + addition;
  }

  double _checkForDecimal(String? decimal, String? alpha) {
    if (decimal != null && decimal.isNotEmpty) {
      return double.parse(decimal);
    }

    if (alpha != null && alpha.isNotEmpty) {
      if (alpha.contains("extra")) {
        return 0.99;
      }
      if (alpha.contains("omake")) {
        return 0.98;
      }
      if (alpha.contains("special")) {
        return 0.97;
      }
      final trimmedAlpha = alpha.replaceFirst('.', '');
      if (trimmedAlpha.length == 1) {
        return _parseAlphaPostFix(trimmedAlpha[0]);
      }
    }

    return 0.0;
  }

  double _parseAlphaPostFix(String alpha) {
    final number = alpha.codeUnitAt(0) - ('a'.codeUnitAt(0) - 1);
    if (number >= 10) return 0.0;
    return number / 10.0;
  }
}